This project is designed to evaluate the potential developmental toxicity of xenobiotics using the whole embryo culture technique. The system supports the normal growth and development of rodent embryos in an in vitro system and allows for the evaluation of the effects of an agent on the developmental processes. Ethanol has been reported to be an animal and human developmental toxicant: however, the proximate toxicant has not been determined. This project has shown that short exposure periods (equal to the half Life of ethanol in vivo) to high concentrations of ethanol (equal to the peak serum concentration produced from doses that produce malformations in vivo) do not produce high rates of neural tube defects in vitro. This suggests that an ethanol, as a single agent, may not b proximate toxicant following short-term exposures. There is a positive correlation between the area under the time concentration curve and the incidence of neural tube defects in vitro.